How to Dress a Baby for Sleep, by Room Temperature

Above 20°C, a short-sleeved bodysuit or just a nappy is enough. Charts are useful and every one of them is an approximation. This post gives you the chart, then tells you where it stops applying.

Key facts

• 16 to 20°C is the recommended room temperature range for infant sleep, because overheating raises the risk of SIDS.
• Check temperature at the chest or back of the neck. Hands and feet run cool on a perfectly comfortable baby.
• Hats come off indoors. Babies lose heat through the head, and a covered head is an overheating risk.
• One blanket folded in half counts as two.
• Never layer two sleeping bags. Air trapped between them adds far more warmth than the TOG numbers suggest.
• Weighted sleeping bags and swaddles are not recommended under one year.

The chart

• Above 24°C - 0.5 tog sleeping bag, or none. Underneath: a short-sleeved bodysuit, or just a nappy.
• 21 to 23°C - 1.0 tog. Underneath: a short-sleeved bodysuit.
• 18 to 20°C - 2.5 tog. Underneath: a long-sleeved bodysuit or sleepsuit.
• 16 to 17°C - 2.5 to 3.5 tog. Underneath: a sleepsuit over a long-sleeved bodysuit.
• Below 16°C - 3.5 tog. Underneath: a sleepsuit plus a bodysuit, and warm the room if you can.

An honest note about that table. TOG-to-temperature charts are a manufacturer convention, not official guidance. Safe-sleep organisations explain what TOG means and deliberately stop short of prescribing a value per degree, because babies differ, rooms differ, and a chart invites people to trust a number over the child in front of them. Use it as a starting point, then check.

What TOG actually measures

TOG is a measure of thermal insulation. The higher the number, the more warmth the item traps. It says nothing about the fibre, the fit, or how breathable the material is - two bags with the same TOG can behave very differently on a warm night.

That last point is where fibre matters, and it is the part most guides skip.

Why wool behaves differently from the chart

A TOG rating measures insulation under dry, still conditions. Real babies produce moisture, and what a fabric does with that moisture decides how a night actually feels.

Wool absorbs moisture as vapour into the fibre itself - a substantial share of its own weight - without feeling wet against the skin, and releases it slowly. The practical effect is a buffer: temperature swings in the room, and a baby's own damp patches, are evened out rather than transmitted straight through. Synthetic fleece and, to a lesser degree, cotton hold moisture at the surface instead, which is why a baby in a synthetic bag can end up clammy at the same TOG and temperature where a wool one stays dry.

Wool also keeps insulating when damp, which cotton does not.

None of that exempts you from the maths. A 2.5 tog wool bag is still a 2.5 tog bag and can still overheat a baby in a warm room. What wool buys you is a wider comfortable band and fewer sweaty wake-ups within it, not permission to ignore the temperature.

The check that overrides everything

Put your hand flat on your baby's chest, or the back of their neck, under whatever they are wearing.

• Hot or sweaty: remove a layer. Overheating is the risk that matters.
• Cool chest: add a layer.
• Cold hands and feet with a warm chest: entirely normal. Do not add layers because of cold feet.

Do this on the first night of any change - new bag, new season, heating on for the first time - and then trust what you learned.

Signs to act on: sweating, damp hair, flushed cheeks, rapid breathing, a hot chest or neck. A baby who is too hot will often be restless before they are sweaty.

A note on the 16°C figure

UK safer-sleep guidance gives 16 to 20°C. French guidance is more commonly cited as 18 to 20°C, and you will see both across Europe.

They are not really in conflict. Both are aimed at the same thing - preventing overheating - and the lower end of the UK range assumes a baby dressed for it. In practice, if your room sits at 17°C in winter, that is fine with a sleepsuit and a warmer bag. Chasing 20°C with the heating is neither necessary nor better.

What matters far more than the exact number is that the room is not creeping above 20°C without you noticing, which is what happens with heating in winter and, more dangerously, during a heatwave.

Heatwaves

The advice inverts, and in southern Europe this is the situation that actually causes problems.

Above 24°C, strip back rather than layer. A short-sleeved bodysuit is usually enough; above around 26 to 27°C, a nappy alone is fine. Skip the sleeping bag entirely if the room is hot, or drop to 0.5 tog.

Keep shutters and curtains closed through the day, air the room hard at night and early morning when outside is cooler than inside, and use a fan to move air around the room rather than pointed at the cot. Offer extra feeds - babies lose more fluid in heat and cannot ask.

And check more often than you think you need to. Rooms that were fine at bedtime can climb several degrees by two in the morning during a heatwave.

The rest of safer sleep, briefly

Dressing is one part of it. The others, which no amount of correct layering substitutes for:

• On the back, for every sleep, until they can roll both ways reliably.
• Feet at the foot of the cot, so they cannot wriggle under bedding.
• A firm, flat mattress and a clear cot - no pillows, duvets, bumpers, or soft toys for the first year.
• Nothing over the face or head.
• Smoke-free, before and after birth.

If any of this is new or you are unsure, your midwife or PMI nurse is the right person to ask, and this post is not a substitute for that conversation.

Frequently asked questions

What room temperature is best for a baby?

16 to 20°C is the recommended range, and French guidance commonly cites 18 to 20°C. Both aim to avoid overheating, which is the real risk.

How do I know if my baby is too hot?

Feel the chest or the back of the neck. Hot or sweaty skin means remove a layer. Cold hands and feet are normal and not a sign of being cold.

What TOG do I need at 20 degrees?

Conventionally a 2.5 tog bag with a long-sleeved bodysuit or sleepsuit, though TOG-to-temperature charts are manufacturer convention rather than official guidance. Check the chest on the first night and adjust.

Can my baby wear a hat to sleep?

No. Hats should be removed indoors, because babies release heat through their heads and a covered head can cause overheating.

Can I put a blanket over a sleeping bag?

No. If your baby feels cold, add a clothing layer or use a higher TOG bag instead.

Is wool better than cotton for baby sleepwear?

Wool manages moisture better and buffers temperature swings, so it tends to give a wider comfortable range. It does not change the TOG maths or the need to check.

Related reading

• Why wool doesn't need washing
• How many clothes does a newborn actually need?
• European baby clothing sizes explained

Sources

The Lullaby Trust, "How to dress your baby for sleep" and "Room temperature" guidance. This post is general information and not medical advice - follow the guidance of your midwife, health visitor, or PMI.